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I installed Mint 10 Mate with unetbootin on my Lenovo S10-3t and tried to update to Mint 14 Mate, but when I try to update with Update Manager, It won't update any files. It always says that the issue is a Failed to fetch ... 404 Not found. For example:

I can't even connect to the wireless network so I am currently sharing my internet connection with my MacBook Pro using an Ethernet cable.

Could that be the issue and if so, how can I resolve this? It is still running Mint 10 Mate. I tried installing Mint 14 Mate but the Lenovo wasn't recognizing the USB drive. Said it wasn't bootable even though I used unetbootin with the Mint 14 Mate x64 iso with it.

You should be able to boot of of a USB drive. I have that laptop and have installed mint 13 from a USB drive. Maybe unetbootin didn't do a good job. I've had that happen before. Just delete all the files on the USB and try unetbootin again.